Why are the manatees dying?
And why you should care
The Florida manatee is a highly unique and charismatic marine mammal that lives along the coast of the eastern United States. In summers, the subspecies can range as far north as Massachusetts, as far west as the Gulf coast of Texas, and as far south as the Florida Keys (other subspecies populations live further south in the islands of the Caribbean and down to Brazil). In winters, however, the entire population returns to Florida to freshwater springs and powerplant outflows, since the species cannot survive in water temperatures below 72°F. The need to congregate in warm water springs has an economic benefit for Florida — every year tourists flock to places like Three Sister Springs near Homosassa, FL to swim with these gentile giants. It also means that manatees require healthy rivers, oceans, and every aquatic environment in between to thrive as a species. This makes them an ideal sentinel species for the Florida’s aquatic ecosystems — a species of animal whose population can be an indicator of overall ecosystem health.
Luckily, given their utility as a sentinel species, Florida manatees are also one of the most closely studied marine mammals in the United States. The Florida Fish and Wildlife Conservation Commission (FWC) performs a necropsy (animal autopsy) on nearly every Florida manatee that dies. This has been critical in helping reduce deaths due to watercraft injuries, since an increase in deaths from boat strikes in an area can clearly demonstrate a need for increased slow boating zones. It also, makes it easy to track population trends and quickly discover threats to the species and has been a significant driver of the environmental protections that have returned the species from near extinction in the 20th century.
While the past 30 years have been an unqualified victory for Florida manatees, with the population ballooning from just over 1,000 animals in 1991 to an estimated 6,000 today, the past year has been a different story. Over 800 animals have died so far in 2021, a mortality total generally seen over a year, rather than in 6 months. Unusual mortality events (UMEs), the technical term for abnormal increases in deaths in a species, have happened before in the Florida manatee, but the current UME is concerning due to its size, cause, and implications. The 2021 deaths are predominantly located on the east coast of Florida, specifically in and around the Indian River Lagoon. According to FWC, these deaths are primarily due to the loss of seagrass in the area, the primary food source for manatees. The manatees are starving to death.
The problem is entirely human caused, resulting from years of prioritizing short term economic growth over protecting the very environment that makes Florida such an attractive place to live and visit. The natural flow of water along the Florida peninsula is south, from Lake Okeechobee down through the Everglades and out to sea. Unfortunately, the area just south of the Everglades has become heavily developed for both housing and agriculture, particularly the politically connected sugar industry. To protect this development, a series of canals were built to divert water east and into rivers that flow into the Indian River Lagoon. In dry years most of the water still flows south from the lake, but in years with heavy rains, it is now discharged to the east to prevent what would otherwise be devastating flooding to these developed areas. The issue is compounded by the fact that Lake Okeechobee has become an ecological calamity in and of itself — nutrient runoff from fertilizer and other agricultural waste has resulted in dangerously high nitrogen and phosphorous levels and nearly constant cyanobacterial blooms. The lake is so polluted that the Army Core of Engineers has proposed the radical and costly step of sucking out the muddy bottom from the entire lake — an area of almost 470,00 acres.
Unsurprisingly, this lake water discharge has been a disaster for the Indian River Lagoon. The nutrients in the water trigger vast algal blooms that can be seen from space, and which block out light to the seagrass, preventing them from photosynthesizing and starving them to death. Many of these algae, like Karenia brevis or the many species of cyanobacteria, produce toxins that are deadly to both animals and people. These blooms can last months to even years and leave in their wake millions of dead animals and billions of dollars of economic damage. Algal blooms also tend to grow quickly then die, with their decomposition by other microscopic organisms depleting all the oxygen in the area. This produces vast “dead zones”, suffocating fish, shrimp, mussels, crabs, snails, and anything else that cannot escape quickly enough from the area or can’t breathe air. The final damaging piece of the puzzle comes from the salinity of the water itself. Most species of aquatic organisms tolerate only a small range of salinity before they can no longer properly regulate their internal electrolytes and die. This is true for animals and seagrasses alike, and sudden drops in salinity are a major factor in the seagrass mortality in the Indian River Lagoon.
Seagrass is a species that makes up the foundation of coastal ecosystems in Florida, and the loss of these plants are a problem for more than just manatees. The plants provide critical habitat for everything from scallops to fish to sea turtles, and its loss damages the entire coastal ecosystem. Unfortunately, over the past 10 years alone, over half of the seagrass in the Indian River Lagoon has been killed. The manatee deaths this year are just one symptom of the larger ecosystem collapse in the Lagoon. This is an economic disaster as well as an environmental disaster. The Florida economy is highly dependent on a healthy environment, with the Florida recreational fishing industry alone being worth over $10 billion annually. For too long, short-term development has taken precedence over long term ecosystem health in Florida. The problems surrounding Lake Okeechobee will take decades and billions of dollars to reverse, but it is critical that it happens. Florida voters already recognize the need to change business as usual, with multiple taxpayer-funded restoration plans having been voted for in state wide referendums. One of these plans involves purchasing land south of Lake Okeechobee to return it to wetlands and restore the natural flow of water in south Florida. The Florida legislature now needs to get on board and vote to implement the restoration efforts. We need to do this to help the manatees and their environment, but ultimately the biggest benefactor may be the millions of people who live around the Indian River Lagoon.
